I guess you haven't been following that the Oscorp building was going to be in Avengers but they had finished post-production on the city skyline so that hint/link was cut-out.. Marvel Entertainment helped the production of Amazing Spider-Man tenfold compared to the original Sam Raimi films..if you look at the new Spider-Man cartoon they already set him up to join S.H.I.E.L.D. his parents had been revealed in the comics as agents..wouldn't be shocked if that's the big reveal in The Amazing Spider-Man sequels.. yes Sony owns him but having him in Avengers sequels is an excellent way to promote the Spidey brand and sell more tickets to future solo films.. X-Men producer Lauren Shuler Donner already wants to have their mutant characters join the Avengers.. so why wouldn't Sony do the same if it only helps their films?

there's also Norman Osborn who get's control of S.H.I.E.L.D. and turning it into H.A.M.M.E.R. I mean there are a few angles they could bring Spidey into the fold.. as long as Sony was able to use things in their films like naming characters and sharing S.H.I.E.L.D... it could open the door to a bigger Marvel Cinematic Universe.. something I believe is already happening over at Fox with The Wolverine ushering in their new shared universe similar to how Spidey is being rebooted he could easily slide into the world of the Avengers..Feige has mentioned Civil War for Avengers 3 and they'll need characters like Wolverine and Spider-Man for something like that.

I knew about the Oscorp thing, but that was merely the image of a building, not a character. These studios jealously guard their sole right to use the Marvel characters they have licensed because of the monetary and legal concerns. While allowing crossovers between studios might seem logical to fans, there are so many complex legal issues involved that none of the other studios is ever likely to allow it.

You have only to look at the example of Marvel trying to bargain with Fox for the right to use Galactus & The Silver Surfer in its films. Marvel was willing to allow Fox to keep the rights to Daredevil longer than their contract allowed in exchange for use of the characters. Even with that major concession on the table, Fox refused to accept the deal. Fox allowed Daredevil's rights to revert to Marvel, even though they had a director and writer hired for the reboot, rather than simply share a couple of characters on a limited basis.

Now I ask you, does that make it seem likely that the other studios will ever be willing to allow their characters to appear in Marvel films? Allowing villains from the Fantastic Four to appear in Marvel Studios' films would have been an excellent promotional opportunity for Fox, particularly in light of how poorly its previous FF films fared at the box office. Yet they passed on the deal, and in the process gave up another franchise as well. There must be some very powerful legal disincentives preventing deals like this from being made. Therefore, I don't think a crossover is ever going to happen.